This invention relates to a syringe and in particular to a plastic syringe suitable for use as a prefilled product.
Prefilled plastic syringes are known. These syringes are disposable and are more convenient than disposable syringes which require filling before use as they come as a single dose product already accurately filled and labelled with the name of the injectable. These syringes are also safer as there is a lower risk of incorrect dosing on administration as well as a lower risk of transfer of transmissible viruses which may otherwise occur on transfer of the injectable from a separate ampoule.
Typically, prefilled syringes include a barrel containing an injectable solution and a plunger assembly. The barrel includes a closure at one end sealing an outlet opening and incorporates an opening at the other end in which the plunger assembly is located. The plunger assembly includes a stopper which seals the opening and further includes a plunger shaft which is connected to the stopper and which extends outwardly from the barrel. The syringe may also include an integral needle fitting at the closure end to provide a support for a hypodermic needle. The syringe may also incorporate other fittings, such as a luer lock finish to enable the syringe to be connected to other complementary fittings, such as those used with an intravenous drip. Examples of previous prefilled syringe designs are described in the applicant""s earlier Australian Patents 595096 and 635631.
Being a prefilled product, it is important that the injectable be safely housed within the barrel. While previous prefilled syringes have maintained the injectable in an aseptic environment, the syringe has been susceptible to tampering after filling. Prefilled syringes are often used for the supply of narcotic substances intended to be delivered intravenously for therapeutic use. The supply of narcotic substances to hospitals, doctors and like persons is strictly controlled and such products are usually available only on prescription from a qualified medical practitioner. Organisations such as hospitals, control distribution carefully and generally narcotics are held in a cupboard or room to which there is limited access. Theft of narcotics is a major problem as there is a ready market of persons prepared to pay substantial premiums for restricted drugs.
An aim of the present invention is to provide a prefilled plastic syringe design which is more tamper resistant and tamper evident than previous designs.
According to the present invention, there is provided a plastic prefilled syringe including a syringe body and a plunger assembly, the syringe body having opposed first and second ends and an inner wall defining a cylindrical chamber which contains an injectable solution, the first end of the syringe body being sealed by a closure and the second end incorporating an opening, the plunger assembly including a plunger shaft extending through said opening and a stopper secured at an end of said shaft within said chamber, the plunger assembly being movable within the chamber with the stopper being operable to seal the opening wherein the plunger assembly includes barrier means on said shaft, the barrier means being adapted, in conjunction with a part of the syringe body, to inhibit access to the injectable solution through the opening.
In one form, the barrier means is of substantially the same diameter as the cylindrical chamber of the syringe body and is thus adapted in conjunction with the inner wall of the chamber to restrict access to the injectable solution. In this embodiment of the invention, there is minimal clearance between the peripheral edge of the barrier means and the inner wall. This inhibits location of a conduit, such as a hypodermic needle along the interface between the stopper and the inner wall. Preferably in this arrangement, the barrier means is in spaced relationship to the stopper and the clearance between the barrier means and the inner wall is 0.3 mm or less. Most preferably it is between 0.1 to 0.3 mm.
In another form, the syringe body includes an annular abutment surface which extends inwardly from the inner wall at or adjacent the opening and the barrier means is adapted in conjunction with the abutment surface to restrict access to the injectable solution. In this embodiment of the invention the barrier means preferably extends outwardly from the shaft at a location intermediate the abutment surface and the stopper and is preferably in overlapping arrangement with the abutment surface so as to prevent removal of the plunger assembly from the syringe body. In this context and further in this specification the term xe2x80x9coverlapping arrangementxe2x80x9d is used to mean that the diameter of the barrier means is greater than the distance between opposite sides of the abutment surface. The overlapping arrangement inhibits a conduit such as a hypodermic needle being inserted into the injectable solution along the interface between the plunger assembly and the inner wall. A hypodermic needle is generally not flexible enough to bend about the abutment surface and the barrier means in a manner which would allow further movement of the head of the needle between the inner wall of the syringe and the stopper.
In a particularly preferred arrangement, the syringe is designed such that the barrier means is adapted to restrict access to the injectable solution in conjunction with both the abutment surface and the inner wall.
The applicant has realised that in previous syringe designs, the interface between the plunger assembly and the syringe body made the syringe susceptible to tampering as it was possible to locate a conduit, such as a hypodermic needle, along this interface into a position where the needle tip was in contact with the injectable solution. Once in this position, the injectable can be withdrawn through the needle and if desired, replaced by another solution such as a saline solution. Furthermore the needle could be withdrawn without marking the syringe body or plunger assembly to leave very little or no evidence of tamper.
An advantage of the preferred forms of the present invention is that the barrier means inhibits access to the injectable. In particular, the barrier means inhibits the insertion of a needle along the interface between the plunger assembly and the syringe body due to the minimal clearance between the barrier means and the inner wall and the overlapping arrangement between the abutment surface and barrier means. Furthermore, if an attempt is made to force the needle through the barrier means, then the needle is likely to be bent and/or become blocked thereby preventing withdrawal of the injectable. In addition any attempt to access the injectable by a needle is likely to mark the barrier means. Such marking provides evidence of tamper which is noticeable to an end user of the syringe and alerts them to the fact that the syringe has been tampered and that it should not be used. This improves the safety of the product and also assists in controlling distribution of the injectable solution.
Preferably the barrier means is in the form of a disc which extends about the shaft. Preferably the disc is integrally formed with the shaft during manufacture of the plunger assembly.
Preferably the syringe body includes a collar at the second end which defines an opening which is narrower than the diameter of the cylindrical chamber. In a preferred arrangement, the free end of the collar extends inwardly from the inner wall of the chamber to provide the abovementioned abutment surface. Preferably in manufacture of the product, the free end of the collar is located in its inward extending position after placement of the plunger assembly within the chamber and typically, this is done by a thermo forming operation.
Preferably the stopper is connected to the end of the shaft. In one arrangement the stopper is mounted on a threaded stud formed at the end of the shaft. Preferably the stud is engagable within a recess formed in the stopper which incorporates a complementary threaded arrangement. Preferably the shaft also incorporates a disc adjacent the threaded stud which extends outwardly from the shaft and which is adapted to abut the stopper. The disc may form the barrier means. Alternatively in a preferred embodiment this disc with a second but spaced disc also located on the shaft and of similar size, together form the barrier means.
To minimise the material used in the manufacture of the shaft, it is preferable that the shaft is formed from a plurality of interconnected fins which extend outwardly from a central axis of the shaft. The fins are angularly spaced about the axis with their free ends defining the outer dimensions of the shaft. In a preferred arrangement, the shaft further includes at least one web which extends transverse to the shaft axis and which interconnects adjacent fins. Preferably these webs extend substantially to the free end of the respective fins. The advantage of this arrangement is that these webs further inhibit the placement of a needle along the interface between the plunger assembly and the syringe body and thereby further improve the tamper resistance of the syringe.
Preferably the syringe of this invention is made from elastomer such as polypropylene, polyethylene or polyethylene terephthalate. Most preferably, it is injection molded from polypropylene.